By doping with rare earths, YAG (═Y3Al5O12) becomes a solid laser oscillation material, and although researched extensively, the majority of studies have used monocrystals. Nonetheless, recent findings have revealed that sintered ceramics can impart equivalent characteristics, and therefore research and development worldwide, especially in Japan, is taking up approaches to solid laser materials based on transparent ceramics that have superior cost advantages.
Reviewing the research history, the YAG family first appears when the hydrothermal synthesis of (Y, Tb, Dy, Ho, Yb)3Al5O12 was reported in Russia in 1967. They used sodium carbonate and chlorides of the constituting elements, and, briefly, conducted additional research on the synthesis conditions for Y3Al5O12 and garnets such as Y3Ga5O12, Nd3Ga5O12, Sm3Ga5O12 under high temperature and pressure of 500° C. or more and several thousand atmospheres, but the reaction system itself was not water and steam pressurization, and the reaction was clearly promoted by a method of applying gas pressure externally (B. V. Mill, Kristallografiya, Vol. 12, No. 1, pp. 158-160, 1967, and B. V. Mill, “Hydrothermal Synthesis of Aluminum and Gallium Garnets”, Sov. Phys.-Crystallogr., Vol. 12, No. 1, pp. 137-139, 1969). Moreover, there were research reports on the hydrothermal synthesis of YAG at about that time (R. C. Puttbach et al., “Hydrothermal Growth of Y3Al5O12”, Proceedings of the International Conference on Crystal Growth, pp. 569-571, 1967 and E. D. Kolb and R. A. Laudise, “Phase Equilibria of Y3Al5O12, Hydrothermal Growth of Gd3Ga5O12 and Hydrothermal Epitaxy of Magnetic Garnets”, Journal of Crystal Growth, Vol. 29, pp. 29-39, 1975), but these were the same regarding the reaction system. Then, there was nothing at all in these articles regarding the concept of space filling with polyhedron microparticles.
Subsequently in 1986, hydrothermal synthesis was conducted using special source materials, and Tb:YAG crystal microparticles having several forms were synthesized (T. Takamori and L. D. David, “Controlled Nucleation for Hydrothermal Growth of Yttrium-Aluminum Garnet Powders”, Am. Ceram. Soc. Bull., Vol. 65, Issue 9, pp. 1282-1286, 1986). In this method, a chloride solution or citric acid solution is spray dried in the first stage, the crystal nucleation density is next adjusted by heating, and then hydrothermal synthesis is conducted in an autoclave, and therefore the process was extremely complicated and non-productive. Further, the present invention, which directly precipitates crystals from the solution phase is fundamentally different.
As a part of the development of new luminescent microparticles, an application was submitted for Tb:YAG microparticles in 1989 (U.S. Pat. No. 5,037,577). The method described here was different from that of the aforementioned Russian research group and that of T. Takamori and L. D. David, Am. Ceram. Soc. Bull., and was hydrothermal synthesis from a simple aqueous solution, specifically, yttrium-aluminum garnet microparticles were produced by allowing a hydrolytic degradation product of an yttrium compound or yttrium salt, and a hydrolytic degradation product of an aluminum compound or aluminum salt to react in an alkali aqueous solution of pH 10.0 or more at a reaction temperature of 270° C.
However, although U.S. Pat. No. 5,037,577 is substantially the same type as the present invention in the procedures of producing hydrothermal microcrystal particles, the present invention is a technical conception related to the point of not only synthesizing these microparticles, but also of controlling the exterior shape thereof and somehow obtaining a sintered body with a polyhedron filled structure. U.S. Pat. No. 5,037,577 did not study this point at all.
Since 1995, Sandia National Laboratories has reported hydrothermal synthesis of YAG-Tb for low acceleration voltage displays (M. L. F. Phillips and L. E. Shea, “Effects of Processing on the Low-Voltage Performance of Cathodoluminescent Garnet Phosphors”, International SAMPE Technical Conference, pp. 501-506, 1995 and M. L. F. Phillips and B. G. Potter, Jr., “Photo- and Cathodoluminescence of hydrothermally Synthesized Y3Al5O12:Tb and NaY(WO4):Tb”, Ceramic Transactions, Vol. 67, pp. 89-103, 1996). Nonetheless, all of these differ from the common method of hydrothermal synthesis, and resemble the flax method in which the substance in solution is heated at 500° C., and then this amorphous body is loaded in an autoclave and processed in the vicinity of 600° C. Consequently, this manufacturing method is vastly different from the hydrothermal synthesis method founded on liquid phase. In 1997, these authors broadened the range of the synthesis compositions beyond YAG:Tb to GGG:Tb and YGG:Tb, but the manufacturing method was not changed (L. E. Shea et al., “Phosphor Synthesis Routes and Their Effect on the Performance of Garnet Phosphors at Low-Voltages”, Materials Research Society Symposium Proceedings, Vol. 424, pp. 409-414, 1997). Of course, there was no description of a special stage relating to the shape of the microparticles and to techniques of making sintered bodies thereof.
Further, there were reports of obtaining spherical particles of YAG:Tm, Tb, Eu through a sol-gel method as luminescent materials for low acceleration voltage displays (R. P. Rao, “Synthesis of Fine Grain YAG:RE3+ Phosphors for Low Voltage Display Devices”, Proc. SPIE, Vol. 2651, pp. 139-146, 1996), but with thermal processing at 1200° C. and the like, it would be difficult to say that this is a preferable method in terms of industrial applicability.
More recently, Adschiri et al. of Tohoku University applied the broad range of reactivity of ultracritical fluids to microparticle synthesis, and reported the synthesis of barium hexaferrite and of Tb doped YAG microparticles as reported in the past using special linked syntheses equipment (Y. Hakuta et al., “Continuous Production of Phosphor YAG:Tb Nanoparticles by Hydrothermal Synthesis in Supercritical Water”, Materials Research Bulletin, Vol. 38, pp. 1257-1265, 2003, T. Haganuma et al., “Synthesis of Phosphor(YAG:Tb) Fine Particles by Hydrothermal Synthesis in Supercritical Water”, Koatsuryoku no Kagaku to Gijutsu, Vol. 10, p. 98, 2000, T. Adschiri et al., “Hydrothermal Synthesis of Metal Oxide Fine Particles at Supercritical Conditions”, Industrial & Engineering Chemistry Research, Vol. 39, pp. 4901-4907, 2000, T. Adschiri, “Material Synthesis in Supercritical Water-Specific Features of Reactions in Supercritical Water and novel Processes for Organic and Inorganic Syntheses-”, Zairyo-to-Kankyo, Vol. 49, pp. 126-129, 2000, Y. hakuta et al., “Production of Phosphor (YAG:Tb) Fine Particles by Hydrothermal Synthesis in Supercritical Water”, Journal of Materials Chemistry, Vol. 9, pp. 2671-2674, 1999, T. Adeshiri, Chemical Engineering, Vol. 43, No. 11, pp. 817-824, 1998, T. Adschiri, “Production of Metal Oxide Fine Particles via Hydrothermal Synthesis under Supercritical Conditions”, Ceramics, Vol. 35, No. 7, pp. 534-537, 2000). Nonetheless, this is special equipment, and problems appear to remain in terms of production characteristics and uniform conditions. Moreover, although Japanese Unexamined Patent Publication No. 2000-129255 describes a manufacturing method going through hydrothermal processing of terbium-activated indium aluminum oxide luminescent material (including compositions with a garnet structure) applicable to forming uniform and dense high-intensity luminescent films for cathode ray tubes, luminescent lamps, plasma display panels and field emission displays, it is difficult to say that the production characteristics are applicable as a manufacturing method.
A Korean group formed by Pusan University and LG Electronics has studied Tb:YAG synthesis conditions in the alkali region using KOH and NH4OH, and have obtained 0.2μ YAG particles in a reaction at 350° C. for 12 hours. Further, they have synthesized the composition zone of (TbxY1-x)3Al5O12, but all of these are no more than synthesis of microparticles in the same way as U.S. Pat. No. 5,037,577, and there has been no investigation on the point of obtaining a sintered body with a polyhedron filled structure by controlling the external form. (S-H. Gee et al., Han'guk Seramik Hakhoechi, Vol. 37, No. 8, pp. 739-744, 2000 and S-M. Kim et al., Han'guk Seramik Hakhoechi, Vol. 37, No. 8, pp. 745-750, 2000)
Japanese Unexamined Patent Publication Nos. 2001-187884, 2002-226844, 2002-371273, 2002-371274, 2003-013057, 2003-034786, 2003-034788, 2003-034789 and 2003-034790 are well-known to contain expertise relating to the hydrothermal synthesis of luminescent materials. However, the luminescent materials claimed in this patent literature are luminescent materials that emit in the visible region by ultraviolet ray excitation, and are fundamentally different than the present invention because these materials are not used in a high-density sintered form, and are limited to used as a powder.
Meanwhile, well-known manufacturing methods of luminescent material with pigment that are related to hydrothermal synthesis include Japanese Unexamined Patent Publication Nos. 5(1993)-331461, 5(1993)-331462, 6(1994)-033051 and 6(1994)-041526. The targeted materials therein are a material group with mCoO.nAl2O3 (m/n=0.9) cobalt blue pigments mixed in a ZnS:Ag, Cl blue emitting luminescent material group, and luminescent material of Y2O3:Eu with adhered colcothar, and the content and objectives differ from those of the present invention.
Knowledge on manufacturing of luminescent material by hydrothermal synthesis is disclosed in Japanese Unexamined Patent Publication No. 9(1997)-291279 regarding ZnGa2O4 crystals, and in U.S. Pat. No. 5,893,999 regarding LaPO4:Ce,Tb luminescent material. Nonetheless, not only are the crystal structures of these materials not the garnet structures, C-rare earth structures, A2SiO5 structures, perovskite structures or gadolinium orthoferrite (GdFeO3) structures that are the focus of the present applicant, but there were no disclosures relating to sintering, and the like. Thus, these inventions are completely different than the present invention.
Moreover, in regard to functional materials using a hydrothermal synthesis (processing) method, Japanese Unexamined Patent Publication Nos. 3(1991)-159917 and 2000-001397 disclose the hydrothermal synthesis of a rare earth iron garnet material as a coated magnetooptic recording medium; and Y. S. Cho et al., “Hydrothermal Preparation and Morphology Characteristics of Y3Fe5Ol2”, Journal of the American Ceramic Society, Vol. 80, Issue 6, pp. 1605-1608, 1997 discloses the same hydrothermal synthesis of Y3Fe5O12 (═YIG) material. Described in this literature are materials having a garnet structure, which is one of the crystal structures addressed by the present applicant, but because of the large visible range absorption based on the admixture of Fe ions, these materials are not suitable for use in ceramic materials that oscillate when excited by semiconductor lasers, or in light-emitting ceramic materials that adjust the color tone of a semiconductor light emitting diode when excited by light emitted from a semiconductor light-emitting diode; and are different than the materials of the present invention.
Meanwhile, when investigating translucent ceramics, there is Japanese Unexamined Patent Publication No. 5(1993)-139862, which attempts to obtain a transparent ceramic after producing PLZT microparticles by hydrothermal synthesis, but these PLZT microparticles are an optically passive material, and are not a light-emitting, luminescent material. In addition, Japanese Unexamined Patent Publication No. 5(1993)-139862 does not disclose sintering using a polyhedron particle as the departure raw material, does not include the technical concept of the uniformity of the particles of the sintered body, and differs greatly from the present invention.
Looking at the worldwide situation, the group of A. Ikesue et al. and the joint research group of Yanagitani and Haneda comprise the two main foundations in the development of inventions relating to transparent ceramic laser oscillator materials for solid lasers. The work of these groups will be explained below.
In Japanese Unexamined Patent Publication No. 5(1993)-301770, the group of A. Ikesue et al. describes as a polycrystal transparent ceramic for lasers a sintered body having a garnet structure with 1% or less porosity comprising one or two or more kinds in SiO2, Li2O, Na2O, MgO, or CaO, and one or two or more kinds in a lanthanide element, Cr element, or Ti element as a light-emitting element. Described in Japanese Unexamined Patent Publication No. 5(1993)-294724 a polycrystal transparent YAG ceramic for a solid laser in which 50 to 20000 weight ppm of one type or more of a fluoride compound comprising a group of YF3, AIF3, NaF, MgF2, CaF2, or LiF is added as sintering aid. However, the ceramics described in Japanese Unexamined Patent Publication Nos. 5(1993)-301770 and 5(1993)-294724 are manufactured by a process different from the method of using crystalline microparticles from hydrothermal synthesis in the departure raw material, and do not require a uniform particle shape or particle diameter in the ceramic sintered body; and the attempt is to promote as high a density as possible by the effects of the aforementioned additives and methods of adjusting the departure raw materials, which is different from the present invention.
Moreover, inventions related to materials for transparent YAG or garnet crystal structure raw material laser oscillators include: Japanese Unexamined Patent Publication No. 3(1991)-218963 that stipulates a process similar to the common solid phase reaction and several sintering additive; Japanese Unexamined Patent Publication No. 5(1993)-175591 that stipulates a laminate structure of monocrystal YAG and polycrystal YAG ceramics; Japanese Unexamined Patent Publication No. 5(1993)-235462 that stipulates a YAG manufacturing method based on a solid phase reaction process that stipulates the specific surface area of Al2O3 and Y2O3 powders, which are the raw materials; Japanese Unexamined Patent Publication No. 5(1993)-286761 that stipulates the amount of oxide synthesizing components of Li2O, Na2O, MgO, CaO, and SiO2 as sintering aids; Japanese Unexamined Patent Publication No. 5(1993)-286762 that stipulates the use of one or more kinds of YF3, AlF3, NaF, MgF2, CaF2, and LiF fluorides as additional sintering aids; Japanese Unexamined Patent Publication No. 5(1993)-294709 that stipulates the mean particle size of the ceramic sintered body after production; Japanese Unexamined Patent Publication No. 5(1993)-294722 that stipulates that raw material Al2O3 and Y2O3 powders be used with respective primary particle sizes of 0.1 to 5 μm and 0.01 to 2 μm; Japanese Unexamined Patent Publication No. 5(1993)-294723 that stipulates the primary particle size and oxide components of Li2O, Na2O, MgO, CaO, and SiO2 as sintering aids; Japanese Unexamined Patent Publication No. 5(1993)-301769 that claims a garnet structure containing F ions; Japanese Unexamined Patent Publication No. 5(1993)-335678 that broadly describes one or more kinds of lanthanide elements, Cr and Ti elements, YAG monocrystals for lasers containing 0.005 to 1 weight % Si elements, and the range of impurities; Japanese Unexamined Patent Publication No. 6(1994)-211563 that stipulates a polycrystal transparent ceramic for laser nuclear fusion having a garnet structure; Japanese Unexamined Patent Publication No. 2001-220223 that stipulates the manufacturing process such as the stage of obtaining Y2O3 in which Nd is uniformly distributed; Japanese Unexamined Patent Publication No. 2003-267797 that stipulates and mentions small tilt grain boundaries and dislocation density; Japanese Unexamined Patent Publication No. 5(1993)-330912 that relates to polycrystal transparent Y2O3 ceramic for lasers, which is a ceramic other than one with a garnet structure, with a stipulated porosity, particle size and the like; Japanese Unexamined Patent Publication No. 5(1993)-330913 that relates to polycrystal transparent Y2O3 ceramic for lasers, which in addition to mean particle size and porosity, stipulates one or more kinds of ThO2, HfO2, ZrO2, Li2O, LiF, BeO and Al2O3 as well as additives and the like; and Japanese Unexamined Patent Publication No. 6(1994)-211573 that relates to a Y2O3 manufacturing method that stipulates a reaction using powder consisting of molded body density of 94% or more prior to sintering. Further publications include: A. Ikesue et al., “Fabrication of Polycrystalline, Transparent YAG Ceramics by a Solid-State Reaction Method”, J. Am. Ceram. Soc., Vol. 78, Issue 1, pp. 225-228, 1995, A. Ikesue et al., “Fabrication and Optical Properties of High-Performance Polycrystalline Nd:YAG Ceramics for Solid-State Lasers”, J. Am. Ceram. Soc., Vol. 78, Issue 4, pp. 1033-1040, 1995, A. Ikesue et al., “Synthesis of Nd3+, Cr3+-codoped YAG Ceramics for High-Efficiency Solid-State Lasers”, J. Am. Ceram. Soc., Vol. 78, Issue 9, pp. 2545-2547, 1995, A. Ikesue and K. Kamata, “Role of Si on Nd Solid-Solution of YAG Ceramics”, J. Ceram. Soc. Japan, Vol. 103, Issue 5, pp. 489-493, 1995, A. Ikesue et al., “Effects of Neodymium Concentration on Optical Characteristics of Polycrystalline Nd:YAG Laser Materials”, J. Am. Ceram. Soc., Vol. 79, Issue 7, pp. 1921-1926, 1996, A. Ikesue and K. Kamata, “Microstructure and Optical Properties of Hot Isostatically Pressed Nd:YAG Ceramics”, J. Am. Ceram. Soc., Vol. 79, Issue 7, pp. 1927-1933, 1996, A. Ikesue et al., “Optical Scattering Centers in Polycrystalline Nd:YAG Laser”, J. Am. Ceram. Soc., Vol. 80, Issue 6, pp. 1517-1522, 1997, A. Ikesue and K. Yoshida, “Scattering in Polycrystalline Nd:YAG Lasers”, J. Am. Ceram. Soc., Vol. 81, Issue 8, pp. 2194-2196, 1998, A. Ikesue and K. Yoshida, “Influence of Pore Volume on Laser Performance of Nd:YAG Ceramics”, J. Mater. Sci., Vol. 34, pp. 1189-1195, 1999, A. Ikesue et al., “Development and Prospect of Ceramics Laser Elements”, Laser Review, Vol. 27, No. 9, pp. 593-598, 1999, A. Ikesue et al., “High-Performance Microchip Lasers Using Polycrystalline Nd:YAG Ceramics”, Journal of the Ceramic Society of Japan, Vol. 108, Issue 4, pp. 428-430, 2000, A. Ikesue, “Ce:YAG Ceramics Scintillator for Electron Beam Detector”, Journal of the Ceramic Society of Japan, Vol. 108, Issue 11, pp. 1020-1023, 2000, A. Ikesue and Y. Sato, “Synthesis of Pr Heavily-Doped, Transparent YAG Ceramics”, Journal of the Ceramic Society of Japan, Vol. 109, Issue 7, pp. 640-642, 2001, V. Lupei et al., “Laser Emission under Resonant Pump in the Emitting Level of Concentrated Nd:YAG Ceramics”, Applied Physics Letters, Vol. 79, No. 5, pp. 590-592, 2001, V. Lupei et al., “Spectroscopy and Laser Emission under Hot Band Resonant Pump in Highly Doped Nd:YAG Ceramics”, Opt. Commun., Vol. 195, pp. 225-232, 2001, V. Lupei et al., “High-Resolution Spectroscopy and Emission Decay in Concentrated Nd:YAG Ceramics”, Journal of the Optical Society of America B, Vol. 19, No. 3, pp. 360-368, 2002, A. Ikesue et al., “Structure of Nd:YAG Ceramics Having Ultra-Low Scattering and the Development of High Performance Lasers Using Polycrystal Media”, FC Report, Vol. 20, No. 8, pp. 192-197, 2002, Y. Sato et al., “Spectral Parameters of Nd3+—ion in the Polycrystalline Solid-Solution Composed of Y3Al5O12 and Y3Sc2Al3O12”, Japanese Journal of Applied Physics, Vol. 42, Part 1, No. 8, pp. 5071-5074, 2003, A. Lupei et al., “Energy Transfer Processes of Nd3+ in Y2O3 Ceramic”, J. Lumine., Vols. 102-103, pp. 72-76, 2003, J. Saikawa et al., “Absorption, Emission Spectrum Properties, and Efficient Laser Performances of Yb:Y3ScAl4O12 Ceramics”, Applied Physics Letters, Vol. 85, No. 11, pp. 1898-1900, 2004, and V. Lupei et al., “Single Crystal and Transparent ceramic Nd-doped Oxide Laser Materials: a Comparative Spectroscopic Investigation”, J. Alloys and Compounds, Vol. 380, pp. 61-70, 2004. However, the ceramics described in the patent and non-patent literature above fundamentally differ from the present invention on the point that crystalline microparticles obtained by hydrothermal synthesis, which is synthesis directly in liquid phase, are not taken as the departure raw materials as previously described.
On the other hand, regarding the joint research group of Yanagitani and Haneda: described in Japanese Unexamined Patent Publication No. 2(1990)-092817 is a manufacturing method of yttrium aluminum garnet that stipulates the effect of using a specific “urea precipitation method”, in which an acidic aqueous solution comprising yttrium ions and aluminum ions is neutralized with urea to cause a precursor of YAG microparticles to precipitate; in Japanese Unexamined Patent Publication No. 2(1990)-283663 is described a translucent polycrystal yttrium aluminum garnet and manufacturing method thereof that stipulates translucent polycrystal yttrium aluminum garnet in the early phase in which the Y element of yttrium aluminum garnet Y3Al5O12 is substituted with 0.1 to 5 atomic % of a group comprising lanthanide elements and Cr elements with an atomic number of 58 to 71, and 100 to 2500 wtppm of SiO2 by weight ratio is added; and in Japanese Unexamined Patent Publication No. 4(1992)-055363 is described a translucent polycrystal yttrium aluminum garnet sintered body and manufacturing method thereof that stipulates the mol ratio of Y2O3 and Al2O3, and the fluorine content in the sintered body. However, the YAG described in Japanese Unexamined Patent Publication Nos. 2(1990)-092817, 2(1990)-283663 and 4(1992)-055363 fundamentally differ from the present invention on the point that crystalline microparticles obtained by hydrothermal synthesis, which is synthesis directly in liquid phase, are not taken as the departure raw materials as previously described.
In addition, well-known inventions related to laser oscillator materials comprising transparent YAG or garnet crystal structure material include: Japanese Unexamined Patent Publication No. 1(1999)-093404 that stipulates a urea precipitation method that causes precipitation once an acidic aqueous solution comprising yttrium ions and aluminum ions has been neutralized with urea; Japanese Unexamined Patent Publication No. 10(1998)-067555 that is a translucent ceramic with a garnet crystal structure having main components of Al2O3 and Y2O3, and stipulates the size of the standard production Gibbs energy (ΔGf°); Japanese Unexamined Patent Publication No. 10(1998)-101333, characterized in that a salt such as ammonium carbonate is used in the presence of sulfate ions, and insoluble salts comprising yttrium ions and aluminum ions are crystallized; Japanese Unexamined Patent Publication No. 10(1998)-101334 that describes a method in which hydroxyl acid is contained in a mineral acid salt aqueous solution of yttrium and aluminum, and then a precipitate is obtained by neutralizing with urea and is taken as an yttrium aluminum garnet raw material powder; Japanese Unexamined Patent Publication No. 10(1998)-101411 that stipulates that a YAG precursor is crystallized by adding a mineral acid salt aqueous solution of yttrium salt, aluminum salt and garget composition into an alkaline carbonate aqueous solution, and then is sintered; Japanese Unexamined Patent Publication No. 10(1998)-114519 that stipulates thoroughly cleaning a precipitate obtained by a urea method until the non-related negative ion concentration is 2000 wtppm or less; Japanese Unexamined Patent Publication No. 11(1999)-147757 that stipulates a translucent ceramic that is a garnet structure compound comprising the composition formula M3Al5O12, and M comprises at least Er, Tm, Ho, Dy, Lu, and Tb; U.S. Pat. No. 6,200,918 that stipulates a high corrosion-resistant rare earth aluminum garnet ceramic with a Tm, Yb, Lu total content of 10 to 100 mol %; Japanese Unexamined Patent Publication No. 2000-290066 that stipulates a Y3Al5O12 polycrystal translucent ceramic as a material applied to semiconductor parts requiring additional resistance to chemical corrosion and resistance to plasma; Japanese Unexamined Patent Publication No. 2001-158660 that stipulates the pore concentration and linear transparency of a sintered body having a garnet structure represented by the general formula R3Al5O12 (R is any one type of rare earth element selected from Y, Dy, Ho, Er, Tm, Yb, and Lu); Japanese Unexamined Patent Publication No. 2003-020288 characterized by a junction with a polycrystal body, and the free face when forming a cast molded body is taken as the junction surface; U.S. Patent Application Publication No. 20030214986 that stipulates a compound laser rod having plastic deformation on the periphery of the laser rod and covered by an integrated garnet structure layer and a Re2O3 structure layer; Japanese Unexamined Patent Publication No. 11(1999)-157933 that stipulates comprising Y2O3, a translucent ceramic of R2O3 (R represents a rare earth), and an additive of CaO or MgO as a ceramic with a structure other than that of garnet; U.S. Pat. No. 6,825,144 stipulated by the transparency, Al content and Si content of a sintered material expressed by the general formula R2O3 (R is at least one element of the group comprising Y, Dy, Ho, Er, Tm, Yb, and Lu); Japanese Unexamined Patent Publication No. 2003-128465 stipulated by the Al content and linear transparency of a scandium oxide (Sc2O3) translucent sintered body; and Japanese Unexamined Patent Publication No. 2003-207638 that relates to a polarized light beam splitter for a liquid crystal display using an yttria ceramic. Further publications include: M. Sekita et al., “Optical Spectra of Undoped and Rare-Earth-(═Pr, Nd, Eu, and Er) Doped Transparent Ceramic Y3Al5O12”, Journal of Applied Physics, Vol. 69, Issue 6, pp. 3709-3718, 1990, J. Lu et al., “High-Power Nd:Y3Al5O12 Ceramic Laser”, Japanese Journal of Applied Physics, Vol. 39, Part 2, No. 10B, pp. L1048-L1050, 2000, J. Lu et al., “Highly Efficient 2% Nd:Yttrium Aluminum Garnet Ceramic Laser”, Applied Physics Letters, Vol. 77, No. 23, pp. 3707-3709, 2000, J. Lu et al., “Optical Properties and Highly Efficient Laser Oscillation of Nd:YAG Ceramics”, Applied Physics B, Vol. 71, pp. 469-473, 2000, J. Lu et al., “72 W Nd:Y3Al5O12 Ceramic Laser”, Applied Physics Letters, Vol. 78, No. 23, pp. 3586-3588, 2001, J. Lu et al., “Promising Ceramic Laser Material: Highly Transparent Nd3+:Lu2O3 Ceramic”, Applied Physics Letters, Vol. 81, No. 23, pp. 4324-4326, 2002, J. Kong et al., “Diode-Pumped Yb:Y2O3 Ceramic Laser”, Applied Physics Letters, Vol. 82, No. 16, pp. 2556-2558, 2003, J. Lu et al., “Yb3+:Sc2O3 Ceramic Laser”, Applied Physics Letters, Vol. 83, No. 6, pp. 1101-1103, 2003, A. A. Kaminskii et al., “New Data on the Physical Properties of Y3Al5O12-Based Nanocrystalline Laser Ceramics”, Crystallography Reports, Vol. 48, No. 3, pp. 515-519, 2003, A. A. Kaminsukii et al., “Refractive Indices of Laser Nanocrystalline Ceramics Based on Y3Al5O12”, Crystallography Reports, Vol. 48, No. 5, pp. 868-871, 2002, J-F. Bisson et al., “Laser Damage Threshold of Ceramic YAG”, Japanese Journal of Applied Physics, Vol. 42, Part 2, No. 8B, pp. L1025-L1027, 2003, A. Shirakawa et al., “Diode-Pumped Mode-Locked Yb3+:Y2O3 Ceramic Laser”, Optics Express, Vol. 11, No. 22, pp. 2911-2916, 2003, and K. Takaichi et al., “Highly Efficient Continuous-Wave Operation at 1030 and 1075 nm Wavelengths of LD-Pumped Yb3+:Y2O3Ceramic Lasers”, Applied Physics Letters, Vol. 84, No. 3, pp. 317-319, 2004. However, the descriptions of the patent and non-patent literature above fundamentally build upon the fact that a departure raw material is manufactured by a urea precipitation method that obtains a precipitate product by adding urea to a metal salt mixed solution, or by a method that causes precipitation by ammonium carbonate and ammonium sulfate, and these methods differ vastly from that of the present invention, which manufactures a departure raw material using hydrothermal synthesis that synthesizes in direct liquid phase.
Meanwhile, the group of Ikegami et al. at the Inorganic Materials Laboratory has been conducting research related to transparent ceramics that enters into the purview of solid lasers. Described in Japanese Unexamined Patent Publication No. 11(1999)-130428 is an easily sintered yttrium aluminum garnet powder manufacturing method that stipulates using an alkali to cause coprecipitation of a solution comprising yttrium ions and aluminum ions, and then conducting high temperature processing to obtain a powder made of YAG crystal; and in Japanese Unexamined Patent Publication No. 2000-203933 is the manufacturing method of a transparent yttrium aluminum garnet sintered body using a dry mixture method that stipulates the weight % of sulfur to be contained, the primary particle size of the raw material powder, the gas components when sintering, and the like. However, the YAG described in Japanese Unexamined Patent Publication Nos. 11(1999)-130428 and 2000-203933 is one in which the YAG phase is first produced in a solid phase reaction in the sintering process, and is fundamentally different than the present invention in which crystal microparticles, which are the same as the target composition, are taken as the departure raw material.
Further well-known patents include: Japanese Unexamined Patent Publication No. 9(1997)-110420 that describes YAG sintered body production characterized by causing an acid solution comprising yttrium ions and aluminum ions to precipitate at a specified pH, and by subsequently passing through a cleaning process; Japanese Unexamined Patent Publication No. 9(1997)-315865 that stipulates a method of producing transparent yttrium by passing though a process at one end that causes yttrium carbonate to precipitate from solution; Japanese Unexamined Patent Publication No. 10(1998)-273364 that stipulates a method to produce transparent yttrium taking a substance obtained by thermal decomposition as the departure raw material, and calcium is contained therein; Japanese Unexamined Patent Publication No. 11(1999)-189413 that stipulates yttrium thin flake particles are calcinated in the presence of sulfate ions into yttrium hydroxide congealed into a card house shape; Japanese Unexamined Patent Publication No. 11(1999)-278933 characterized in that pre-sintering of a molded body is conducted at a relatively low temperature when calcining yttrium carbonate cleaned with an aqueous solution comprising sulfate ions; Japanese Unexamined Patent Publication No. 11(1999)-278934 that stipulates a manufacturing method that, after precipitating yttrium carbonate from solution, executes control such that when thermally processing a constant equilibrium state is maintained between the carbonic acid gas pressure P CO2 in the atmosphere in the reaction tank and the carbonic acid gas pressure P CO2 in the reaction solution; Japanese Unexamined Patent Publication No. 11(1999)-278935 indicates the range of transparency in an yttrium oxide sintered body, and further stipulates the fluorine content; Japanese Unexamined Patent Publication No. 2000-281428 that stipulates in a transparent magnesia sintered body the mean particle size comprising SiO2 and B2O3 as additives in the desired concentration; Japanese Unexamined Patent Publication No. 2001-270714 that, in a coprecipitation method in the presence of sulfate ions, uses a technique such that no yttrium carbonate is produced during the process; Japanese Unexamined Patent Publication No. 2001-270775 characterized in that thermal processing is conducted on an amorphous phase precipitate obtained by instilment of acid salt aqueous solution of yttrium and aluminum into carbonic acid containing a basic salt water solution in the presence of sulfate ions; and Japanese Unexamined Patent Publication No. 2002-154870 that relates to a transparent magnesium spinel sintered body that, in a coprecipitation method, passes through a process of precipitation in an environment comprising carbonate ions and ammonium ions. Also well-known is T. Tachiwaki et al., “Novel Synthesis of Y3Al5O12 (YAG) Leading to Transparent Ceramics”, Solid State Communications, Vol. 119, pp. 603-606, 2001. However, the descriptions in the patent and non-patent literature above stipulate various types of additives and detailed conditions during processing, but are different than the present invention because crystal microparticles, which are the same as the target composition, are not used as the departure raw material.
Transparent YAG ceramics are also being developed by the group of Murakawa et al. at Kyocera. Concretely, well-known technology includes: a transparent yttrium-aluminum-garnet sintered body and manufacturing method thereof characterized in that at least one type of metal of Fe, W, Mo, Pd, and Ag is contained at 0.01 to 0.1 wt % (Japanese Unexamined Patent Publication No. 6(1994)-144925); a manufacturing method of a transparent yttrium-aluminum-garnet sintered body characterized in that YAG powder of the target composition is mixed in a mixed powder of Y2O3 and Al2O3, which are the raw material powders (Japanese Unexamined Patent Publication No. 6(1994)-122551); a manufacturing method of a transparent yttrium-aluminum-garnet sintered body characterized in that a YAG phase of 10 to 50% is produced during calcination (Japanese Unexamined Patent Publication No. 6(1994)-107456); a manufacturing method of a transparent yttrium-aluminum-garnet sintered body characterized by a process that specifies the range of X-ray diffraction strength ratio of the crystal phases produced between Y2O3 and Al2O3 in the middle of the calcination process (Japanese Unexamined Patent Publication No. 8(1996)-268751); a manufacturing method of a yttrium-aluminum-garnet powder that stipulates the manufacturing process of the YAG to be calcinated after a precipitate is produced by mixing and neutralizing aluminum hydroxide powder and yttrium compound solution (Japanese Unexamined Patent Publication No. 8(1996)-183613); and there are also Japanese Unexamined Patent Publication Nos. 7(1995)-082025, 7(1995)-114342, 8(1996)-203119, 8(1996)-264155, 8(1996)-298099, 8(1996)-322926, 8(1996)-325054, 8(1996)-327845, 9(1997)-045287, 9(1997)-293774, 9(1997)-320524, 10(1998)-064481, 10(1998)-162776 and 10(1998)-236871. In the above patent literature, as in Japanese Unexamined Patent Publication No. 6(1994)-122551 for example, YAG crystals the same as the target crystal structure are used in the departure raw materials, but these are mixed in order to promote a solid phase reaction by providing one type of template, which is vastly different than the present invention that from the beginning uses microparticles having the same structure as the structure of the target crystals as the majority of the departure raw materials.
Further, Japanese Unexamined Patent Publication No. 2001-158620 describes a sintered body using a rare earth-aluminum-garnet micropowder containing a total of 10 to 10000 ppm of at least one type or more among Mg, Si and Ca compounds, and is characterized by YAG microparticles with a specific surface area of 3.5 m2/g or more and a mean particle size of 1.8 μm or less (preferable 600 nm or less); and Japanese Unexamined Patent Publication No. 2000-302543 describes a translucent material, which is a sintered body with a garnet structure to be used in an arc tube of a discharge lamp, that has a surface roughness (Ra) of 1 μm or less and a porosity of 1% or less, and characteristically the crystal particle size thereof is 30 μm or less. However, the technique of space filling is not described at all in this patent literature.
Well-known inventions related to solid lasers include: a description of a solid laser system in which a GaN group semiconductor laser is used, a rare earth (praseodymium, Pr) excites the solid laser material, and the laser is made to oscillate in the wavelength bands of blue (465 to 495 nm), green (515 to 555 nm), and red (600 to 660 nm) (Japanese Unexamined Patent Publication No. 11(1999)-017266), and a co-doping system comprising Pr is also permitted in the solid laser material in Japanese Unexamined Patent Publication No. 11(1999)-017266; a laser diode excitation solid laser with a SHG wavelength conversion element mounted in the system that takes the final oscillation wavelength band as the ultraviolet region (Japanese Unexamined Patent Publication Nos. 2001-036175 and 2001-036176); an ultraviolet laser apparatus that arranges non-linear optical crystals having a cyclic domain inversion structure in a laser co-oscillator system (Japanese Unexamined Patent Publication No. 2001-185795); a color laser display that applies the aforementioned solid laser element to a display (U.S. Pat. No. 6,764,183,); an emission apparatus that takes a GaN group semiconductor as the activation layer and that causes a garnet group luminescent body activated by a rare earth to emit light by one dimensionally and 2 dimensionally lining up a plurality of emission regions of a broad area (Japanese Unexamined Patent Publication No. 2002-009402); and a laser diode excitation solid laser that is a GaN group semiconductor laser, and that causes visible light, the main light to be oscillated, and light of the ultraviolet region, through a wavelength conversion element, to be oscillated by exciting solid laser material doped with at least one type of ion of rare earth holmium (Ho), or samarium (Sm), or europium (Eu), or dysprosium (Dy), or erbium (Er), or terbium (Tb) (Japanese Unexamined Patent Publication Nos. 2002-344049 and 2002-353542). Moreover, described in European Patent Application Publication No. 1 162 705 is the invention of a diode excitation laser characterized by a system that integrates a solid laser and a laser diode that oscillates at a wavelength from 340 nm to 640 nm, and light with a wavelength from 400 nm to 700 nm is oscillated from the solid material. However, Japanese Unexamined Patent Publication Nos. 11(1999)-017266, 2001-036175, 2001-036176 and 2001-185795, U.S. Pat. No. 6,764,183, Japanese Unexamined Patent Publication Nos. 2002-009402, 2002-344049 and 2002-353542, and European Patent Application Publication No. 1 162 705 are all patents describing the configuration of a simple solid laser, and do not discuss particular techniques for solid laser materials.
Regarding semiconductor laser excitation solid laser systems, there are: Japanese Unexamined Patent Publication No. 5(1993)-090693 that relates to a up-conversion laser having a matrix of (Sr, Ca) (La, Gd)AlO4 group crystals; U.S. Pat. No. 5,070,507 that relates to a Ho doped solid laser that is excited by a wavelength of the 1.1 μm band, and oscillates at a wavelength of the 3 μm band; and Japanese Unexamined Patent Publication Nos. 7(1995)-315992, 8(1996)-012498 and 8(1996)-059397 that relate to solid laser crystal materials that cause a laser of the 1.5 to 2.2 μm band, which is an eye-safe wavelength band, to oscillate using LiYF4 group crystals, and YAlO3 group crystals, using garnet group crystals with a wavelength in the 0.98 to 1.05 μm band, and using LiYF4 crystals, and YAlO3 crystals and garnet group crystals with wavelengths in the 0.98 to 1.04 μm band. However, the object of these inventions differ from that of the present invention.
Meanwhile, regarding white light sources with multi-wavelength output obtained by exciting luminescent bodies with LEDs, well-known inventions include: Japanese Unexamined Patent Publication Nos. 10(1998)-242513 and 11(1999)-243232, International Patent Publication No. WO/98/005078, Japanese Unexamined Patent Publication Nos. 2002-198573, 2002-335010, 2003-101081 and 2003-179259, as well as Japanese Unexamined Patent Publication No. 2001-192655, U.S. Pat. No. 6,642,652, Japanese Unexamined Patent Publication Nos. 2002-232002, 2002-317177 and 2003-105336, and U.S. Patent Application Publication No. 20040145308. However, the majority of these inventions are of the form that the luminescent body to be excited by the LED is impregnated with resin as the microparticle, which differs from the present invention that uses a sintered body of uniform microparticles, and on this point the aforementioned patent literature is different from the present invention.